1. Field of the Invention
The present invention relates to a valve device provided with a liquid surface detecting valve employed in a fuel tank, particularly to an adhesion prevention device in a liquid surface detecting valve.
2. Prior Art
In a fuel tank in an automobile the fuel level in the fuel tank is liable to rise suddenly locally in the fuel tank when the automobile starts or stops suddenly or runs on a bad road or on a sloping road, which entails the overflow of the fuel from the fuel tank. A liquid surface detecting valve is provided for preventing the fuel from overflowing a predetermined level of the fuel in the fuel tank.
A conventional liquid surface detecting valve is described with reference to FIG. 3.
A valve casing 3 is fixed to an upper casing 2 of a fuel tank 1. A float chamber 4 is provided in the valve casing 3. The float chamber 4 has openings 6 at a bottom wall 5 thereof for communicating with the fuel in the fuel tank 1 and a valve seat 8 at an upper wall 7 thereof. The float chamber 4 has a float 9 at the inner space thereof which float 9 has a valve 10 at the upper surface thereof. A valve port 11 is disposed at the upper wall 7 over the valve 10 for communicating with the inner space of the float chamber 4 and a port 12 defined over the float chamber 4. The valve seat 8 is provided around the valve port 11.
The valve casing 3 has a by-pass port 13 at the portion opposite the port 12 for communicating with the port 12 and the space in the fuel tank 1. A spring 15 is provided over the by-pass port 13 for urging a relief valve 14 toward the by-pass port 13 so that the relief valve 14 closes the by-pass port 13.
An operation of the conventional liquid surface detecting valve will be described hereinafter.
When the fuel reaches the predetermined level in the fuel tank, the float 9 in the float chamber 4 rises so that the valve 10 seats on the valve seat 8, thereby closing the valve port 11. Consequently, the fuel is prevented from overflowing the fuel tank 1.
When the fuel lowers from the predetermined level, the float 9 lowers so that the valve port 11 is open. Hence, the pressure in the fuel tank 1 is maintained at all times within a predetermined value of pressure.
If the valve 10 of the float 9 is adhered to the valve seat 8 and does not move away or drop from the valve seat 8, the pressure in the fuel tank 1 increases, thereby causing a fuel vapor system to be inconvenient or troublesome or the fuel tank 1 to be deformed. In such a case, the relief valve 14 rises upward against the resilient force of the spring 15 for opening the by-pass port 13 so that the fuel vapor escapes through the port 12 and a canister, not shown, to the atmosphere, whereby the pressure in the fuel tank 1 is controlled under the predetermined value of the pressure.
However, there is a likelihood that the valve 10 will adhere to the valve seat 8 for a long time, whereby the liquid surface detecting valve loses its function. There is also a likelihood that the relief valve 14 will adhere to the by-pass port 13, whereby no adjustment of the pressure is made by the relief valve 14. As a result, there arises the inconvenience of the fuel vapor system or deformation of the fuel tank 1.